The long-term objective of the proposed research seeks to define the precise molecular events involved in GLUT4 translocation in adipose and muscle, the tissues specific for insulin-stimulated GLUT4 trafficking, such that pharmaceutical agents can be developed to specifically activate this pathway and reduce the risk of diabetes and associated cardiac pathologies. The studies proposed will delineate the domains of syntaxin-4, Munc- 18c, VAMP2/3 and Doc2b required for interaction and GLUT4 vesicle trafficking in the absence and presence of insulin. Moreover, this work will provide evidence for the mechanism by which Munc- 18c acts to regulate GLUT4 docking and fusion with the plasma membrane. Information obtained from in vitro studies plus studies of cells in culture will provide a biochemical model to be tested with the Munc- 18c knock-out mice. In sum, the combination of in vitro, in culture, and in vivo experiments will further our understanding of molecular events responsible for mediating the insulin-stimulated translocation of glut4 vesicles in adipose and muscle, and contribute to our overall understanding of vesicle trafficking in general.